Deep diving cetaceans are species of which little is known since they inhabit areas of great depth (more than 500 meters), generally far from the coast and spend much of the time submerged (some species, up to 92% of the weather).

In the Mediterranean Sea we can find up to 4 species of deep divers, the sperm whale (Physeter macrocephalus), the Cuvier’s beaked whale (Ziphius cavirostris), the long-finned pilot whale (Globicephala melas) and the Risso’s dolphin (Grampus griseus), and we can find them in continental slope areas or areas of submarine canyons and steep slopes that favor the presence of their prey.

Unknown and vulnerable species

Currently, on the one hand, the conservation status of the Mediterranean subpopulations of three of these species (the beaked whale, the long-finned pilot whale and the Risso’s dolphin) is unknown, due to the lack of data on them, and on the other hand, the Mediterranean subpopulation of the sperm whale is considered as “Endangered” by the IUCN (International Union for Conservation of Nature). For this reason, and to increase knowledge about the distribution and abundance of these deep-diving species and to be able to work on management measures in the areas where they live, SUBMON, started the AHAB project this June, with the aim of studying their presence in the waters of the northern sector of the Mediterranean Cetacean Migration Corridor.

All these species are considered in Annex IV (Animal and plant species of Community interest) of the European Habitat Directive (92/43 / EEC) as species that require strict protection. And also, at the state level, the beaked whale, sperm whale and pilot whale are included in the National Catalog of Endangered Species and the pilot whale is considered among the listed species of special interest.

Record on duration and depth immersion

Although all these species belong to the odontoceti family, and they share a great adaptability to dive deep and be able to hold their breath for long periods of time, each one has very different characteristics and capacities. For example, the sperm whale is capable of diving for more than an hour and reaching a depth of 2,000 meters. But it is the Cuvier’s beaked whale, the cetacean that has recorded the deepest dive (2,992m) and the longest dive (2 hours and 17 minutes). The pilot whales, on the other hand, do not make such long dives but they can dive more than 500m. To be able to do this, these species have had to adapt their body and physiology to an extreme situation of high pressure and lack of oxygen, and have modified the way to store, distribute and use oxygen in the body.

The Mediterranean species

Sperm Whale (Physeter macrocephalus):

The sperm whale is the largest species in the odontoceti family, reaching up to 16 meters long. It is a common species in the Mediterranean, where it has a preference for deep waters near the continental slope, and submarine canyon areas.

This species feeds mainly on cephalopods, such as squid, that they find in these deep waters. Males are generally solitary individuals, while females coexist in groups made up of adult females with juveniles and young.

How do we identify it?

The sperm whale is an animal with a dark gray coloration, with an extremely large head (1/3 of the total length of its body) and rough skin behind the head and on the sides. The triangular dorsal fin is transformed into a small hump. This species has an asymmetric blowhole located on the left side of the head, which causes its breath to come out tilted 45º to the left, allowing this species to be easily identified in the distance. In addition, this is the only cetacean species in the Mediterranean that, when submerged, takes its tail out of the water (part of the body that is used for photo-identification) on a regular basis.

Threats

The subpopulation present in the Mediterranean is subject to great pressure from human activities such as collisions with boats, gillnetting with fishing nets, plastic intake and underwater noise.

Risso’s dolphin (Grampus griseus):

The Risso’s dolphin is considered a regular inhabitant of the Mediterranean, although it is a species of which very little is known. In the Mediterranean, this species is known to prefer areas with steep slopes and underwater canyons, and its diet is mainly based on squid.

How do we identify it?

It is characterized by its gray body covered with marks and white scars resulting from social interactions with individuals of the same species. These animals are born completely gray but with age they acquire more scars until they become white. Its head is also characteristic, rounded and does not present the typical “beak” of dolphins.

Threats

The main threats to this species are driftnet gillnets, underwater noise, and plastic intake.

Cuvier’s beaked whale (Ziphius cavirostris):

The Cuvier’s beaked whale, the quintessential deep-sea diver, is a species found in temperate, tropical, subtropical waters of all oceans and is the only species of this common family in the Mediterranean Sea. This species can be seen throughout the year, it prefers deep waters of canyons and seamounts, and solitary individuals or groups of between 1 and 3 individuals are observed. Their long dives and short periods of time on the surface mean that very little is currently known about these animals.

How do we identify it?

It is a large odontoceto (between 5 and 6.5 meters), the color of the body varies with age, so that the animals go from having a dark brown, gray-brown body to animals with a pattern of yellowish-brown coloration. The adult male specimens have a large number of scars on the body and as they age the head becomes whitish. It has the slightly falcate triangular dorsal fin located in the posterior third of the body.

Threats to the species

These animals are very sensitive to underwater noise, with noise derived from military activities being one of the greatest threats to them, generating mass stranding of this species. Other known threats include bycatch in fishing nets, ingestion of plastics, and possibly chemical contamination.

Long-finned pilot whale (Globicephala melas)

The long-finned pilot whale is a species of cetacean that can be found mainly in the western Mediterranean basin, in areas over 500m deep, although very little is known about its movements in the Mediterranean.

How do we identify it?

These animals are characterized by their black body, except in the ventral part where they present a characteristic extensive white spot, they have a low dorsal fin and fall backwards, relatively large located in a central position of the body.

Threats to the species

Very little is known about the threats to the pilot whale in Mediterranean waters. Among others, the most common threats are accidental capture, maritime traffic, chemical and noise pollution, and climate change.

All these species have been detected in the waters of the Mediterranean Cetacean Migration Corridor by SUBMON during the AHAB project and the data obtained will contribute to increasing knowledge about these species